Mobile communications involve, among various processing procedures, signal transmissions and handling of data traffic between an access network (AN) and an access terminal (AT). An access network (AN) comprises many elements, one of which being a base station, as known by those skilled in the art. An access terminal (AT) can be in many forms, including a mobile station (e.g., a mobile phone), a mobile terminal (e.g., a laptop computer), and other devices (e.g., a personal digital assistant: PDA) having the combined functionality of both a mobile station and a mobile terminal, or having other terminal capabilities. Hereinafter, an access terminal (AT) will be referred to as a “mobile” for the sake of brevity.
In a conventional mobile communications system, a plurality of mobiles (e.g., cellular phones, portable computers, etc.) are served by a network of base stations, which serve to allow the mobile stations to communicate with other components in the communications system. Various types of mobile communications systems are known, including Code Division Multiple Access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), and various enhancements and improvements thereto which are generally referred to as next generation mobile communications systems.
CDMA is most widely accepted and continues to develop and evolve. In particular, CDMA technology evolution (such as the so-called “cdma2000” technology or other next generation CDMA systems) will provide integrated voice with simultaneous high-speed packet data, video and video conferencing capabilities. Currently, the third generation (3G) evolution of cdma2000 1× wireless communications is being reviewed or partially adopted by certain standards bodies, such as 3GPP and 3GPP2 (The Third Generation Partnership Project 2).
For example, a baseline framework for cdma2000 1xEV-DV (1xEVolution—Data and Voice) was recently reached by the 3GPP2. The 1xEV-DV standard will be backward compatible with existing CDMA IS-95A/B and CDMA2000 1× systems, allowing various operators seamless evolution for their CDMA systems. Other types of systems that are evolving from CDMA include High Data Rate (HDR) technologies, 1xEvolution—Data Only (1xEV-DO) technologies, and the like, which will be explained in more detail hereinafter.
The present disclosure focuses on data transmission techniques between base stations and mobiles. Thus, a detailed description of additional components, elements and processing procedures (not specifically mentioned herein) have been omitted so that the features of the present invention are not obscured. One skilled in the art would have understood that various other components and techniques associated with base stations and mobiles already known in the art but not described in detail herein, are also part of the present invention. For example, specific details of the protocol architecture having an air interface with a layered structure, physical layer channels, protocol negotiation and processing, and the like have been omitted.
In a communications system, a set of “channels” allow signals to be transmitted between the access network (e.g., a base station) and the access terminal (e.g., a mobile) within a given frequency assignment. Channels consist of “forward channels” and “reverse channels.”
Signal transmissions (data transmissions or transfers) from the base station to a mobile via a downlink (i.e., forward channels) are commonly referred to as the “forward link,” while signal transmissions from the mobile to the base station via an uplink (i.e., reverse channels) are commonly referred to as the “reverse link.”
So-called “physical layers” provide the channel structure, frequency, power output, modulation, and encoding specifications for the forward and reverse links. The “forward channels” consist of those physical layer channels transmitted from the access network to the access terminal, and “reverse channels” consist of those physical layer channels transmitted from the access terminal to the access network.
Of the many portions of the forward and reverse channels, the “forward MAC channel” is the portion of the forward channel dedicated to medium access control (MAC) activities. The forward MAC channel consists of the reverse power control (RPC) channel, the reverse activity (RA) channel, and other channels. Here, the forward MAC reverse activity (RA) channel indicates the activity level (e.g., the load) on the reverse channel.
In the so-called Interim Standard 95A (IS-95A) systems, the forward link and the reverse link are allocated separate frequencies and are independent of one another. For code division multiple access (CDMA) technology is the basis for Interim Standard 95 (IS-95) and can operate in both the 800-MHz and 1900-MHz frequency bands. In CDMA systems, communications between users are conducted through one or more cells/sectors, which are serviced by base stations. A user of a first mobile communicates with another user on a second mobile by transmitting voice and/or data on the reverse link to a cell/sector. The cell/sector receives the data for routing to another cell/sector or a public switched telephone network (PSTN). If the second user is on a remote station, the data is transmitted on the forward link of the same cell/sector, or a second cell/sector, to the second remote station. Otherwise, the data is routed through the PSTN to the second user on the standard phone system.
A mobile communications system can employ connectionless network services in which the network routes each data packet individually, based on the destination address carried in the packet and knowledge of current network topology. The packetized nature of the data transmissions from a mobile allows many users to share a common channel, accessing the channel only when they have data to send and otherwise leaving it available to other users. The multiple access nature of the mobile communications system makes it possible to provide substantial coverage to many users simultaneously with the installation of only one base station in a given sector.
The transfer of digital data packets differs from the transfer of digital voice information. Full duplex (simultaneous two-way) voice communication patterns imply that the data, transferred between the base station and a particular mobile station, are real-time and substantially equal in bandwidth. It has been noted that a total delay of 200 msec (about 2 Kbits of digital data for most speech vocoders) represents intolerable latency within a voice channel. On the other hand, transfer of digital data packets is typically asymmetrical, with many more packets being sent from the base station to a particular mobile via a downlink (the forward link), than from the mobile to the base station via an uplink (the reverse link).
In high speed data packet transfers, users appear to be tolerant of data transfer latencies or delays, with latencies of up to 10 seconds being encountered in current wireless data systems. While such delays appear to be tolerated by the user, the delays, attributable to relatively low effective data transfer rates, are undesirable. One proposed solution, known as “CDMA/HDR” (Code Division Multiple Access/High Data Rate), uses various techniques to measure channel data transfer rate, to carry out channel control, and to mitigate and suppress channel interference.
Conventional CDMA systems must handle both voice and data. To handle voice signals, the delay between the time that information is sent and the time that the information is received must be kept relatively short. However, certain communications systems used mostly for handling data packets can tolerate relatively longer delays or latencies between the time that information is sent and the time that the information is received. Such data handling communications systems can be referred to as High Data Rate (HDR) systems. The following description will focus on HDR systems and techniques, but those skilled in the art would understand that various other mobile communications systems and techniques for handling high data rates, such as 1xEV-DO, 1xEV-DV, and the like, fall within the scope of the present disclosure.
In general, a High Data Rate (HDR) system is an Internet protocol (IP) based system that is optimized for transmitting data packets having bursty characteristics and not sensitive to latencies or delays. In HDR systems, a base station is dedicated to communicating with only one mobile station at any one time. An HDR system employs particular techniques allowing for high-speed data transfers. Also, HDR systems are exclusively used for high-speed data transfers employing the same 1.25 MHz of spectrum used in current IS-95 systems.
The forward link in an HDR system is characterized in that the users are not distinguished in terms of orthogonal spreading codes, but distinguished in terms of time slots, whereby one time slot can be 1.67 ms (milliseconds). Also, on the forward link of an HDR system, the mobile (access terminal AT) can receive data services from about at least 38.4 Kbps to about at most 2.4576 Mbps. The reverse link of an HDR system is similar to the reverse link of an IS-95 system, and employs a pilot signal to improve performance. Also, traditional IS-95 power control methods are used for providing data services from about 9.6 Kbps to about 153.6 Kbps.
In the HDR system, a base station (a part of the access network AN) can always transmit signals at its maximum transmission power, as virtually no power control is required because only one user occupies a single channel at a particular time resulting in practically no interference from other users. Also, in contrast to an IS-95 system requiring an equal data transfer rate for all users, an HDR system need not deliver packet data to all users at equal data transfer rates. Accordingly, users receiving high strength signals can receive services employing high data rates, while users receiving low strength signals can be accorded with more time slots so that their unequal (i.e., lower) data rate is compensated.
In conventional IS-95 systems, because various signals (including pilot signals) are simultaneously transmitted to all users, interference due to pilot signals and undesirably high power consumption are problematic. However, in HDR systems, pilot signals can be transmitted at maximum power because the so-called “burst” pilot signals are employed. Thus, signal strength can be measured more accurately, error rates can be reduced, and interference between pilot signals is minimized. Also, as the HDR system is a synchronous system, pilot signals in adjacent cells are simultaneously transmitted, and interference from pilot signals in adjacent cells can also be minimized.
FIG. 1 shows a portion of a conventional reverse channel structure for sending transmission data rate increase information from a base station to a mobile. A base station (not shown) approximates (or measures) a load on the reverse link, and prepares to send to a mobile (not shown) various messages indicating whether the reverse link load is large or small. A bit repetition means 10 repeats the bits in the messages to be sent a certain number of times to improve signal reliability.
Thereafter, a signal point mapper 11 maps the signal from the bit repetition means 10 by, for example, changing all “0” bits to “+1” and all “1” bits to “−1” to allow further processing. The resulting signal is combined with a so-called “Walsh cover” signal and transmitted over the Reverse Activity (RA) channel to the mobile.
A conventional mobile receives the messages sent by the base station via the RA channel indicating that the current reverse link load is too large, and the mobile reduces the current packet data rate on the reverse link by one-half (½) so that the load on the reverse link is decreased.